KR20180019228A - Method for operating an internal combustion engine - Google Patents

Abstract

The present invention relates to a method for operating an internal combustion engine in which fuel is metered into a combustion chamber of an internal combustion engine directly through a first injection valve into a suction pipe and through a second injection valve, Preferably, the first injection valve is used in the first operation mode and the second injection valve is preferably used in the second operation mode, in which case a minimum amount is metered in by the second injection valve in the first operation mode.

Description

Method for operating an internal combustion engine

The present invention originates from a method of operating an internal combustion engine according to the preamble of claim 1. Objects of the present invention include computer program products.

There is known a method for operating an internal combustion engine in which fuel is metered into a combustion chamber of an internal combustion engine directly through a first injection valve into a suction pipe and through a second injection valve. In this method, the first injection valve is preferably used in the first operation mode, and the second injection valve is preferably used in the second operation mode. This combination of so-called PFI injection and so-called DI injection makes it possible to take advantage of the advantages of the two injection form for optimum mixture formation and combustion. In the full load and dynamic state of the internal combustion engine, it is more preferable to use a second injection valve that directly injects into the combustion chamber. In partial loads, it is preferable to use a first injection valve for injecting into the intake pipe, since in this case less emission is generated.

If the internal combustion engine is operated for a longer period of time in the first operating mode in which it is injected only into the intake pipe, it may occur that the fuel and / or fuel components are deposited on the second injection valve. Such precipitates plate-out within the injection holes and / or on the outer surface of the valve seat. Such precipitates are formed especially at high temperatures. It is already known in the prior art that a method of intermittent injection using a second injection valve prevents or even eliminates the corresponding deposits. The second valve is also cooled not only by the fuel itself, but also by fuel evaporation, which reduces the sticking of the precipitate and the chemical conversion of the fuel.

In comparison to the prior art, the method according to the invention with the features of independent claim 1 has the advantage that the deposit can be prevented or eliminated as much as possible.

According to the present invention, the minimum injection amount is metered in by the second injection valve in the first operation mode. By doing so, sediment formation in the injector can be surely prevented.

Particularly preferably, when the total injection amount is larger than the minimum injection amount, the minimum injection amount is metered in by the second injection valve. In an operating state where the total injection amount is smaller than the minimum amount, there is a possibility that very small sediment is formed. Whereby the control of the injection valve can be excluded. As a result, energy is saved and unnecessary loading of the injection valve is prevented.

Particularly preferably, the minimum injection amount corresponds to the minimum injection amount of the second injection valve. This means that the minimum injection amount is preferably slightly larger than the minimum injection amount.

In another aspect, the present invention relates to source code having program code, particularly a compiler instruction and / or a link instruction, having a processing instruction for generating a computer program that can be executed on a control device, Generates a computer program for executing all the steps of the above-described method when the program code is converted into an executable computer program in accordance with processing instructions, that is, in particular, compiled and / or linked. This program code can be provided in particular by, for example, source code downloadable from a server in the Internet.

Embodiments of the present invention are illustrated in the drawings and described in detail below.
Fig. 1 is a diagram showing the main elements of an injection system having first and second injection valves.
Figures 2-4 are various flowcharts of various embodiments of the method according to the present invention.

In Figure 1, the main elements of the injection system are shown. In Figure 1, only a brief illustration showing only the combustion chamber and associated injection valves has been selected. The present invention is not limited to the application of such an internal combustion engine having one cylinder. The present invention may be used in any number of cylinders.

The combustion chamber of the internal combustion engine is denoted by reference numeral 100. The combustion chamber 100 is supplied with the air or air-fuel mixture through the intake pipe 110. To this end, it is proposed that the fuel is injected into the intake pipe 110 by the first injection valve 120. In addition, a second injection valve 130 is provided which can inject fuel directly into the combustion chamber 100. In the illustrated embodiment, first and second injection valves are assigned to each cylinder of the internal combustion engine. However, only one first injection valve may be provided for all the cylinders or one group of cylinders. In this case, the fuel reaches through one first injection valve into one common suction pipe of several cylinders.

The control unit 140 supplies control signals to the first injection valve 120 and the second injection valve 130. [ The control unit 140 processes the output signals of the first sensor 150 and the second sensor 160. The first sensor preferably detects variables that characterize the operating state of the internal combustion engine. This is, for example, the number of revolutions (N) of the internal combustion engine. The second sensor 160 preferably detects variables that characterize the ambient conditions or the driver's needs. Based on these variables, the control unit 140 computes a control signal for the operation of the injection valve 120 or 130.

Such an injection system is generally referred to as a dual system. The internal combustion engine is preferably operated in the first operating mode in which the injection is performed by the first injection valve 120 within a low engine speed range and load range. Alternatively, within the higher load range and higher engine speed range, a second mode of operation is implemented in which fuel injection is effected substantially through the second injection valve 130. In case of operating for longer in the first operating mode, the risk of coking due to the lack of perfusion and the lack of cooling of the second injection valve 130 associated therewith, and the risk of corking of the second injection valve 130 There is a risk of reducing the amount.

There is also the possibility that the fuel pressure can increase to the maximum pressure in the supply system for the second injection valve 130 due to the temperature rise. At this time, when the switching to the second operating mode is effected, the injection is carried out at such a maximum pressure and at a pressure not optimal for the corresponding operating point. As a result, mixing deviations, increased emissions and quieter running variations can occur due to non-optimal injection times.

From the prior art, it is known to execute switching to the second operating mode after a predetermined time in the first operating mode, in order to avoid coking of the second injection valve. However, such a transition is not optimal for engine operation and, in part, causes a mixed deviation with increased exhaust emissions and quiescent drift, depending on the situation.

In the embodiment described below, the second injection valve is continuously controlled with the adjustable minimum injection time. By doing so, continuous perfusion and cooling can be ensured, whereby coking can be reliably prevented. Further, the pressure in the high-pressure rail can also be set to a desired optimum target pressure. A separate switching from the first operating mode to the second operating mode and a separate switching in the opposite direction is no longer necessary.

However, in the above embodiment, there is a requirement that exhaust gas deterioration should not occur in the dynamic running characteristic by the injection amount as described above. This requirement is ensured in this embodiment by keeping the minimum injection time set for the high-pressure injection valve constant regardless of the total fuel mass required.

The above embodiment is described in detail in the flowchart of Fig. In the first step 200, the possible minimum injection amount Q2min of the second injection valve 130 is calculated from the minimum injection time T2min. Different parameters such as injection pressure, injection angle, fuel density, motor speed, camshaft angle, and crankshaft speed are inserted into this calculation. In this case, it can also be proposed that only one of the above-mentioned parameters is used.

Typically, the calculation of the injection time T is performed based on the injection amount Q. The calculation of the minimum injection amount Q2min based on the minimum injection time T2min is performed based on the same parameters as the ordinary calculation of the injection time T based on the injection amount Q. [ The minimum injection time T2min is the injection time at which the second injection valve 130 can be controlled so that just one injection is performed. In the control under the minimum injection time, (prescribed) injection is not possible.

In the second step 210, the injection quantity for the first injection valve Q1 is calculated starting from the present total injection quantity Q, that is, the injection quantity for the first injection valve is "total injection quantity Q- Quot; minimum injection amount Q2 for the injection valve ". The sum of the injection amount for the first injection valve and the injection amount for the second injection valve in one combustion cycle is referred to as a total injection amount.

In a third step 220, a so-called split factor (Smin) is calculated starting from the two injection quantities for the two injection valves. This split factor directs the dispense amount distribution between the first injection valve and the second injection valve. The thus determined split factor Smin is later used to calculate the final injection amount and time in the normal calculation method for the two fuel paths. The split factor Smin indicates the ratio between the injection quantities of the two injection valves. In this case, the second injection valve is controlled by injecting the minimum injection amount Q2min or by the minimum injection time T2min.

Within the normal fuel path, the operational state of the internal combustion engine is determined at step 230, i.e., the output signals of the various sensors are evaluated. In particular, the variables specified above are used. In the next step 240, the split factor S for the current injection is determined. A subsequent selection step 250 selects the current split factor S or the split factor Smin calculated in step 220. [ This selection is such that the splitting factor S is used if sufficient splashing is possible using the second splitting valve 130 due to the current splitting factor S and that sufficient injection using the second splitting valve 130 is used If not, the split factor Smin from step 220 is made available. If the split factor is defined as the ratio of the injection amount of the second injection valve to the injection amount of the first injection valve, whether or not the split factor Smin is smaller than the split factor S is checked. If the split factor Smin is less than the split factor S, the split factor S is used. If the split factor Smin is greater than the split factor S, the split factor Smin is used.

In step 260, the injection quantity is distributed to the two injection valves due to the split factor selected in step 250. [ Subsequently, the control time of the injection valve is calculated, and then the metering is performed in step 270.

In another embodiment, it has been proposed that the minimum injection amount Qm is continuously supplied to the second injection valve. The deficit for the total injection quantity for the current operating point is injected by the first injection valve. When the total injection amount in the present operating state is smaller than the minimum injection amount Qm of the second injection valve, supply of the minimum injection amount Qm by the second injection valve is no longer provided. This relates, for example, to the situation in the so-called coasting mode of the internal combustion engine or to the situation when the cylinder is switched off. In the present embodiment, an operating state in which no combustion should occur is handled. In this operating state, no heat is introduced into the injector, or very little heat is introduced, whereby the plate-out can be ignored. In the following, the approach is described with reference to the flowchart.

In the first step, the minimum injection amount Qm for the second injection valve 130 is calculated. Further, the total injection amount Q is calculated. In step 300, a difference DQ between the total injection amount Q and the minimum injection amount Qm of the second injection valve is calculated. In step 310, whether the total injection amount Q is larger than the minimum injection amount Qm If the total injection quantity Q is less than the minimum injection quantity Qm in the inquiry step 310, the minimum injection quantity Qm is set to the minimum injection quantity Qm, The minimum injection amount Qm and the injection of the difference DQ by the first injection valve 120 are performed by the second injection valve 130 in step 380. [

Preferably, the minimum injection amount Qm is selected to be slightly greater than or equal to the minimum injection amount Q2min. Preferably, in order to obtain the minimum injection amount Qm, a small value is added to the minimum injection amount Q2min.

In another embodiment, it has been proposed that by a plate-out model, a characteristic parameter characterizing the strength of the precipitate on the injection valve is determined. For this purpose, the property values for deposition or deposition decomposition are integrated. If the characteristic value is positive, deposition occurs. If the characteristic value is negative, deposition decomposition occurs.

In the first improvement example, the characteristic value is determined starting from substantially different operating characteristic variables. The characteristic value characterizes the amount of heat that actually flows into the injection valve. The following parameters are used to determine the following variables: the split factor, the fuel temperature, the engine temperature, the intake air temperature, the intake air mass, the torque or load, the number of revolutions, the installation location and installation conditions of the injector in the engine, One characteristic value is determined by selecting one of the operating modes of the model using the model.

The deposition model considers the various effects on deposition. These effects are the heat flow to the injector surface, the amount of fuel deposited on the surface for each injection, and the temperature level in the injector. The first two variables are particularly related to deposition on the injector surface, and the last parameter relates specifically to deposition in the injector.

Large heat flow into the injector surface results in large characteristic values. The heat flow into the surface substantially depends on the number of revolutions of the internal combustion engine and the load of the internal combustion engine. As the number of revolutions increases, the heat flow also increases. As the load increases, the heat flow also increases. Various variables can be used as the load. These are, among other things, the driver demand signal, the torque variable or the position of the throttle valve. Also, the heat flow increases as the charge motion increases. The reason is that the charge motion can not be directly measured. As a substitution parameter, the position of the charge motion flap or valve control time is used.

The amount of fuel deposited on the surface for each injection is substantially dependent on the parameters described below.

As the number of partial injections per combustion cycle increases, there is less wetting tendency and thereby the amount of fuel deposited is also smaller, thereby resulting in a smaller characteristic value. As the amount of fuel accumulated on the surface increases, the characteristic value decreases.

As the injection duration per partial injection type increases, there is an increasing tendency to wetness, which results in a larger amount of fuel to be deposited, which results in a larger characteristic value. As the accumulated injection duration increases, there is an increasing tendency to wetness, which leads to a larger fuel quantity to be deposited, which results in a larger characteristic value. The accumulated injection period can be understood as a total fuel amount injected in one combustion cycle.

As the temperature level increases over time in the injector, the deposition in the injector increases, thereby also increasing the value of the characteristic. When the number of revolutions and the load of the internal combustion engine are higher, a higher temperature level appears in the injector, whereby a higher possibility of deposition appears, and thus a higher characteristic value appears.

As the fuel temperature increases, the deposition increases, thereby also increasing the characteristic value. If one day of measurement can not be used for the fuel temperature, other temperature values, for example intake air temperature, may be used.

If the control period is longer / longer or the number of partial injections is higher due to the intrinsic heating by the heat of electrical loss heat, a higher temperature level appears in the injector and thus a higher deposition appears, appear.

As the engine temperature rises, the injector temperature also increases. As a result, an increasing characteristic value appears as the engine temperature increases.

The split factor is inserted into the model as follows: As the injection rate using the first injection valve increases, the deposition increases. As the injection rate using the second injection valve is increased, the deposition is reduced or the covering decomposition is increased.

Combustion method or type of operation of the engine

The installation position and the installation state of the injector in the engine, and the compression ratio of the engine are preferably inserted into the model as a constant variable.

As soon as the fact that a characteristic parameter characterizing the strength of the deposit on the injection valve exceeds the threshold is detected, appropriate measures are introduced. In this case, the proportion of the injection amount metered and inputted by the second injection valve increases. Such an increase in the injection quantity ratio is achieved in such a way that the split factor is correspondingly changed.

The action is preferably carried out for a certain period of time. In a particularly preferred embodiment, it has been proposed that the duration of action depends on a characteristic variable.

When the split factor is inserted into the covering model, the action is terminated as soon as the model detects that sufficient covering decomposition has occurred.

In the second improvement example, the characteristic value is determined within a specific load spectrum starting from the operating period. To this end, it is determined how long the internal combustion engine will operate in a particular load spectrum. Each load spectrum is assigned one specific characteristic value. This characteristic value is then multiplied and integrated with the period during which the internal combustion engine is operated within the load spectrum. The characteristic parameter determined in this way is a measure of the strength of the precipitate on the injection valve.

The load spectrum is defined by a range of values for the number of revolutions and a range of values for the torques provided by the internal combustion engine. Each combination of the value range for the number of revolutions and the value range for the torque is assigned one property value for deposition.

As the number of revolutions increases, the property value increases. As the torque increases, the characteristic value also increases. If the value for the number of revolutions or torque is small, the characteristic value takes a negative value in some cases.

As soon as the fact that a characteristic parameter characterizing the strength of the deposit on the injection valve exceeds the threshold is detected, appropriate measures are introduced. In this case, the ratio of the injection quantity injected by the second injection valve increases. Such an increase in the injection quantity ratio is achieved in such a way that the split factor is correspondingly changed.

The action is preferably carried out for a certain period of time. In a particularly preferred embodiment, the duration of the action depends on the characteristic variable.

In Figure 4, this approach is illustrated with reference to a flow chart. The elements already described in Fig. 3 are denoted by corresponding reference numerals. In step 400, the property value is determined using the deposition model. In a following step 410, the characteristic value is integrated and thereby the characteristic variable is calculated. In query step 420, if the fact that the characteristic variable is greater than the threshold value is detected, the split factor is correspondingly changed in step 250.

In a preferred embodiment, it has been proposed that the split factor is moved by a certain amount in the direction of a larger injection quantity for the second injection valve. This situation means that the movement of the split factor is performed only once, but the switching to the injection path using only the second injection valve is not performed at all.

In yet another embodiment, the correction value for the split factor, which is to be added to the split factor for the current operating state that was calculated in step 240 in step 250, is not checked whether the characteristic variable has exceeded the threshold value, . ≪ / RTI > This correction value is determined as a function of the characteristic variable. Preferably, there is a linear relationship between the correction value and the characteristic variable for the split factor. As the characteristic variable increases, the correction factor increases so that a larger injection quantity is metered in by the second injection valve.

Claims (7)

The fuel is metered into the combustion chamber of the internal combustion engine directly into the intake pipe through the first injection valve and through the second injection valve, preferably the first injection valve is used in the first operating mode, A method for operating an internal combustion engine, in which a second injection valve is preferably used,
Characterized in that in the first operating mode a minimal amount is metered in by the second injection valve. The method according to claim 1, wherein when the total injection amount is larger than the minimum injection amount, the minimum injection amount is metered in by the second injection valve. 3. A method according to claim 1 or 2, characterized in that the minimum injection amount corresponds to the minimum injection amount of the second injection valve. 12. A computer program product adapted to perform all the steps of the method according to any one of claims 1 to 3. 5. A machine-readable storage medium storing a computer program according to claim 4. A control device configured to perform all the steps of the method according to any one of claims 1 to 3. A program code having a processing instruction for generating a computer program that can be executed on a control device,
Wherein the program code generates a computer program according to claim 4 when the program code is converted into an executable computer program according to a processing command.

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